Conversion of the titanium values in various titaniferous ores has been accomplished heretofore mainly by single stage chlorination of an ore/carbon mixture under fluidized bed conditions. Usually, the chlorination agent has been elemental chlorine. By-product iron chlorides, especially where the titaniferous ore contains a significant amount of iron, pose a problem in disposal and waste valuable chlorine.
In the present process, advantages are obtained by chlorinating in a two-stage process. In the first stage, a major part of the ore to be processed is chlorinated in a conventional fluidized bed reactor yielding TiCl.sub.4 and iron chloride, mainly FeCl.sub.2. A second smaller portion of the ore is ground (-325 mesh) and chlorinated in a dilute phase reactor with FeCl.sub.2 vapor.
The present process provides an improved process for producing TiCl.sub.4, a product useful in and of itself as a catalyst, or as a precursor to the production of high purity pigment grade titanium dioxide. Problems attendant preparation of the charge and disposal of by-products such as FeCl.sub.x are avoided.
Prior art is mainly concerned with a single stage chlorination process and does not provide a key to a two stage chlorination.
U.S. Pat. No. 2,589,466 to Wilcox discloses a process for removing titanium as titanium tetrachloride from ilmenite ore by heating the ore to a temperature above 1250.degree. C. but below 1500.degree. C., similarly heating chlorine to such a temperature and then bringing the chlorine and ore together in a reaction chamber. The iron contaminant in the ilmenite ore is removed as a solid residue while the TiCl.sub.4 is vaporized out of the reactor.
U.S. Pat. No. 2,657,976 to Rowe et al. show a process for producing iron oxide and titanium tetrachloride from titaniferous iron ores. According to this process, the titanium ore containing iron is subdivided, mixed with carbon and placed in a chamber. Chlorine and moist air are introduced into the chamber to produce at an elevated temperature volatile ferric chloride substantially free from titanium tetrachloride. The amount of chlorine added is the theoretical amount required to react with the iron values but not with the titanium values. Moist air is also added. Ferric chloride is volatilized and separated from the titanium concentrate, and the ferric chloride reacted immediately with oxygen to produce ferric oxide and chlorine gas. The ferric oxide and chlorine so produced are separated and the chlorine returned to react with the titanium values in the concentrate to produce titanium tetrachloride. These reactions take place in a divided reactor.
U.S. Pat. No. 3,067,005 to Nelson et al., discloses a process for chlorinating a ferrotitanate such as ilmenite in a fluid bed reactor. Unreacted chlorine in the gaseous stream rising from the reaction zone is fixed (i.e., converted to a normally solid form) by adding FeCl.sub.2 in particulate form to the stream while the stream is still at a temperature where FeCl.sub.2 reacts with Cl.sub.2 at a convenient speed, i.e., at a temperature in excess of 700.degree. C. The resulting FeCl.sub.3 at once sublimes and joins the off-gas stream from, which it can be readily separated. This process is adaptable for use in the present primary chlorination stage.
U.S. Pat. No. 3,105,736 to Groves discloses a process for the chlorination of metal bearing materials in a bed in a zone of chlorination which is improved by establishing a pair of fluidized beds of pulverulent material to be chlorinated suspended in an upwardly flowing stream of gas which is inert to the material. The beds having separate upper levels and being in communication below the upper levels. The upper level of the first bed forms a surface bounded on the one side by the fluid bed and on the other side by an inert fluidizing gas. The upper level of the second bed communicates directly with the zone of chlorination. As more material is fed into the first bed, material flows into the second of the bed and from there into the zone of chlorination by flow of the upper level.
U.S. Pat. No. 3,144,303 to Engelmann discloses a continuous process for the production of volatile metal halides, especially titanium tetrachloride and ferric chloride within a closed reaction vessel at an elevated temperature and in the presence of a gaseous or finely divided solid reducing agent, chlorine and a fluidized bed suspension of a finely divided titaniferous material such as ilmenite or rutile. The temperature and composition of the bed is maintained within optimum operating conditions by means of a dynamic interchange between a portion of the particles of the reactant bed with the particles from a communicating separate auxiliary fluidized bed maintained under control or regulated nonreacting conditions.
U.S. Pat. No. 3,376,112 to Dunn et al. relates to a process for flowing a molten metal salt complex of the formula XFeCl.sub.4 where X is an alkali metal as a thin film over a moving bed of particulate inert material concurrently with an oxygen containing gas and recovering chlorine as a product.
U.S. Pat. No. 3,466,169 to Nowak et al. provides a process for chlorinating an ore in the presence of coke. The amount of chlorine is limited to the stoichiometric amount needed to form the chloride of the metal of greatest chloride forming affinity. The temperature is held above the vaporization point of the resulting chloride. This removes all of the metal of greatest chloride forming affinity from the ore. The resulting chloride gas along with any chloride impurities formed is passed over new ore which is free of carbon at which time chloride impurities are removed in favor of additional chloride of the metal of greatest chloride forming affinity in order to yield pure chloride of the metal of greatest chloride forming affinity. This pure metal chloride may then be reduced to yield metal in the zero valence state and the ore that is then free of all metals of greatest chloride forming affinity can be treated similarly for collection of the chloride of the metal of next greatest chloride forming affinity. TiCl.sub.4 is contemplated according to this process.
U.S. Pat. No. 3,495,936 to Jones discloses a dilute phase chlorination process for titaniferous ores. Here the ores reacted with chlorine and a carbonaceous reducing agent in a dilute phase reactor system to yield metal chloride products, chiefly titanium tetrachloride.
U.S. Pat. No. 3,683,590 to Dunn teaches a process for condensing iron chlorides from a gaseous stream in two steps, the first step being the cooling of the gases to about 675.degree. C. to condense ferrous chloride as a liquid and leaving a gas ferrous residual and then a second step of adding chlorine gas and sodium chloride salt separately wherein the remaining FeCl.sub.2 is oxidized to FeCl.sub.3 which with the initial FeCl.sub.3 is converted to NaFeCl.sub.4 and cooling that product to a temperature above 159.degree. C. This process is useful for recovering iron chlorides from gaseous effluent to minimize air pollution.
According to U.S. Pat. No. 3,787,556 to Piccolo et al., titanium tetrachloride is made by feeding powdered ilmenite or titanium slag to a reactor with a reagent and heating gas streams of chlorine and the combustion products of coal. The reagent is carbon.
U.S. Pat. No. 3,859,077 to Othmer teaches the production of pure titanium dioxide under reducing conditions by a halogen-oxygen interchange between a titanium tetrahalide and an oxide of iron contained in a slag or in an ore, such as ilmenite, at a temperature of 1000.degree. C. The iron and various impurities are volatilized as halides. Solid TiO.sub.2 remains with some impurities which may be washed out with water or an aqueous acid or alkali. The gaseous ferrous halide is then reacted with some or all of the titanium dioxide and a reductant at a temperature above 1550.degree. C. to be reduced to molten metallic iron and to give the gaseous titanium halide which is passed to a first reactor. Only makeup halogen is required.
U.S. Pat. No. 3,925,057 to Fukushima et al. teaches a process for recycling chlorine gas in the selective chlorination treatment of iron oxide ores containing titanium for the purpose of obtaining ores enriched with TiO.sub.2. Here the chlorine gas introduced into the chlorination reaction is converted to ferric chloride by reaction with the iron oxide. The ferric chloride is reconverted to free chlorine by reaction with oxygen in an oxidation process, and the isolated chlorine returned to the chlorination step.
U.S. Pat. No. 3,977,862 to Glaeser teaches the selective chlorination utilizing ferrous chloride alone or in combinations with other chlorinating members notably chlorine, hydrogen chloride or ferric chloride as part or all of the chlorinating agent. An elevated temperature of 950.degree. to 1400.degree. C. is maintained during the chlorination.
U.S. Pat. No. 3,977,863 to Glaeser discloses essentially the same process as in the U.S. Pat. No. 3,977,862.
U.S. Pat. No. 3,977,864 to Glaeser discloses essentially the same reduction/chlorination process for the treatment of titaniferous materials such as ilmenite.
U.S. Pat. No. 3,989,510 to Othmer describes a process including a reactor operating at a high temperature up to 1950.degree. C. which is charged with a mixture of an iron bearing titaniferous ore, silica, a chloride of an alkaline or alkaline earth metal and a solid reductant such as coke. TiCl.sub.4 is produced.
U.S. Pat. No. 4,014,976 to Adachi et al. teaches the production of TiCl.sub.4 by reacting a TiO.sub.2 material having a particle size of 150 mesh with chlorine in the presence of a coarse carbonaceous material in a dilute phase fluidization system.
U.S. Pat. No. 4,017,304 to Glaeser teaches essentially the same process discussed in the three previous Glaeser patents.
U.S. Pat. No. 4,046,853 to Robinson teaches the simultaneous chlorination of the iron and titanium values in an iron-containing titaniferous ores such as ilmenite. Here, the ilmenite is converted to ferrous chloride, but the resulting gaseous effluent is difficult to process to recover the titanium tetrachloride. The iron values in the effluent are partially oxidized to Fe.sub.2 O.sub.3 and FeCl.sub.3 thereby reducing the partial pressure of the ferrous chloride while maintaining the presence of some ferrous chloride to scavenge any chlorine emitted from the chlorination stage. The residual gaseous iron chlorides are condensed and chlorine free titanium tetrachloride may be recovered from the remaining gases.
U.S. Pat. No. 4,055,621 to Okudaira teaches a process for obtaining chlorine from iron chloride from chlorination of titaniferous ore by adding iron oxide to iron chloride in an amount above 10% by weight of the resulting mixture, charging the mixture into a fluidizing roasting furnace for oxidation, any overflow being oxidized in a second reactor. The iron oxide thus obtained is recycled to the primary reactor for controlling the reaction temperature in the furnace.
U.S. Pat. No. 4,140,746 to Turner et al. relates to the recovery of chlorine values from iron chloride produced from the chlorination of titaniferous material containing iron and particularly from the carbo-chlorination of ilmenite which, for example, can be the first stage in the so-called chloride route to form titanium dioxide pigment. The iron chloride which may be ferric chloride or ferrous chloride is subjected to a combination of reduction and oxidation reactions. In the reduction reaction, ferric chloride is dechlorinated to ferrous chloride by a reducing agent suitable for producing a chloride compound for recycle to the chlorination process. In the oxidation reaction ferrous chloride is oxidized to ferric oxide and ferric chloride, ferric chloride being recycled to the reduction reaction. By this method the chlorine values are recovered from the by-product iron chloride by a route which avoids the difficult reaction between ferric chloride and oxygen to produce chlorine and ferric oxide.
U.S. Pat. No. 4,174,381 to Reeves et al. teaches an improved process and an apparatus for producing chlorine and iron oxide in a multistage recirculating fluidized bed reactor wherein ferric chloride in the vapor phase is reacted with an excess of oxygen at temperatures of from 550.degree. to 800.degree. C. The improvement comprises utilizing a reactor that includes an initial "dense" zone and a downstream "dilute" zone. In the dense zone, a fuel is burned, reactants and recirculated iron oxide particles are heated, ferric chloride is vaporized and at least 50% of the ferric chloride is converted to chlorine and iron oxide. In the downstream dilute zone, the conversion of ferric chloride is continued to greater than 95% completion.
U.S. Pat. No. 4,183,899 to Bonsack teaches a process whereby an iron-containing titaniferous material is chlorinated with chlorine and ferrous chloride (FeCl.sub.2) for producing a product stream of titanium chlorides, and by-product metallic iron and ferrous chloride. The iron chloride is separated from the product stream and recycled to the reaction zone. Iron bearing titaniferous ore and carbon pass dilute phase reactor as finely ground mixture in a laminar flow process.
U.S. Pat. No. 4,310,495 to Bonsack teaches a low temperature (less than 800.degree. C.) process for chlorinating titaniferous material in a fluidized bed. A porous carbon reductant having micropores with a pore diameter of less than 20 angstroms is utilized together with conventional titaniferous material and conventional chlorine sources to achieve reaction at the present low temperatures.
U.S. Pat. No. 4,343,775 to Bonsack teaches a flow process for the chlorination of titaniferous materials. This process utilizes a special microporous carbon (anthracite) characterized by having pores with a pore diameter of less than 20 angstroms. Improved reaction rates and completeness of reaction are achieved.
U.S. Pat. No. 4,442,076 to Bonsack dated Apr. 10, 1984 discloses a process for the entrained downflow nonselective chlorination of fine iron-containing titaniferous material with chlorine gas and/or organochlorides in the presence of fine porous coal based reductant powder for obtaining product chlorides of titanium and iron wherein the combined powders are entrained in and flow downwardly through a chlorination zone at a temperature of at least about 800.degree. C. In the present process similar conditions are used except that the chlorinating agent is FeCl.sub.3 instead of chlorine gas or an organochloride. (See also U.S. Pat. No. 4,343,775 to Bonsack, supra.).
As can be seen from the prior art, in various methods for chlorinating rutile, ilmenite titaniferous slags and the like to produce TiCl.sub.4, the above titaniferous materials are used as a single raw material charge and chlorine is generally the chlorinating agent.
In cases (Bonsack U.S. Pat. No. 4,183,899; Glaeser U.S. Pat. No. 3,977,864), where FeCl.sub.2 is used as a chlorination agent in one zone reactor, the thermodynamics are unfavorable and the reaction is far from complete: CO, CO.sub.2, TiCl.sub.4, which are formed on the initial step of the overall reaction, along with residues of chlorine inhibit the reaction.
In the present case, the charge of process ore is divided into two portions, which are treated in different unit operations and are chlorinated with different chlorinating agents in each operation. The first larger portion (70-80%) of the charge is chlorinated with chlorine or a mixture of Cl.sub.2 +FeCl.sub.3 in a conventional fluidized bed operation to yield TiCl.sub.4 and FeCl.sub.2.
The second portion (20-30% of the charge) is chlorinated with FeCl.sub.2, recovered from the first operation, in a dilute phase operation.